Elevated results in a vitamin B 12 assay when using serum separator blood collection tubes

Abstract

Background: In the light of apparently spurious serum vitamin B₁₂ results in some patients, the effect of serum separator sample tubes on serum vitamin B₁₂ values, assayed by the Bayer Centaur analyser, was examined.

Method: Results of parallel assays of serum vitamin B₁₂ in plain (non-gel) serum tubes and serum separator gel tubes were compared. Serum in previously centrifuged gel tubes was mixed in the tube and the effect of that mixing on assay results quantitated. A limited investigation of the effect of tube cap type was also carried out.

Results: Serum vitamin B₁₂ concentration was 54% higher in samples taken into serum separator tubes after re-mixing the serum in the original tube. This effect could be abolished by re-centrifugation.

Conclusions: Use of serum separator tubes may be associated with spuriously elevated serum vitamin B₁₂ concentrations in the Bayer Centaur assay. Laboratories receiving samples for vitamin B₁₂ assay in serum separator tubes that have already been centrifuged should either re-centrifuge the tubes, or aliquot and re-centrifuge serum from the tubes prior to vitamin B₁₂ assay.